Finishing (such as cutting) of the machined surface by the relative movement of the lap and the workpiece under a certain pressure by the abrasive particles coated or pressed onto the lap. Grinding can be used to process a variety of metal and non-metallic materials, the surface shape of the processing is flat, inner and outer cylindrical and conical surfaces, convex, concave spherical, thread, tooth surface and other profiles. The processing precision can reach IT5~01, and the surface roughness can reach Ra0.63~0.01 microns.
The grinding method can be generally divided into three types: wet research, dry research and semi-dry research.
1 Wet grinding: Also known as sand grinding, the liquid abrasive is continuously filled or coated on the grinding surface, and the abrasive continuously slides and rolls between the workpiece and the lap to form a cutting motion. Wet grinding is generally used for coarse grinding, and the fine powder abrasive used has a particle size coarser than W7.
2 dry research: also known as sand embedding, the abrasive is evenly embedded in the surface layer of the lap, only a small amount of stearic acid mixed fat and other auxiliary materials must be applied on the surface of the lap. Dry grinding is often used for fine grinding, and the fine powder abrasive used is finer than W7.
3 Semi-dry research: similar to wet research, the abrasive used is a paste-like paste. Grinding can be done either manually or on a grinder. Before the workpiece is ground, it must be processed by other processing methods to obtain higher pre-machining precision. The remaining grinding allowance is generally 5 to 30 microns.
The lap is a tool for grinding and shaping the workpiece, and at the same time is a carrier for the abrasive. The hardness should be lower than the hardness of the workpiece and have a certain wear resistance. It is usually made of gray cast iron. The metallographic structure of the wet research tool is mainly ferrite; the dry research tool is made of uniform and fine pearlite. A mild steel lap is commonly used when grinding threads below M5 and small workpieces with complex shapes. When grinding small holes and soft metal materials, brass and copper laps are mostly used. The lap should have sufficient rigidity and the working surface should have a high geometric accuracy. The lap is also subject to cutting and wear during the grinding process. If it is operated properly, its precision can also be improved, so that the machining accuracy of the workpiece can be higher than the original precision of the rig.
Correct handling of the trajectory of the grinding is an important condition for improving the quality of the grinding. In plane grinding, general requirements:
1 The movement of the workpiece relative to the lap is to ensure that the length of the grinding stroke of each point on the workpiece is similar;
2 The workpiece trajectory is evenly distributed throughout the surface of the lap to facilitate uniform wear of the lap;
3 The curvature of the motion trajectory should be small to ensure the smooth movement of the workpiece;
4 The trajectory of any point on the workpiece should avoid premature periodic repetition. The picture shows the commonly used plane grinding motion trajectory. In order to reduce the heat of cutting, the grinding is generally carried out under low pressure and low speed conditions. The pressure of rough grinding does not exceed 0.3 MPa, and the pressure of lapping is generally 0.03 to 0.05 MPa. The speed of rough grinding is generally 20 to 120 m/min, and the speed of lapping is generally 10 to 30 m/min.